Eyeworld

EW FEATURE 54 All about IOL calculations • January 2017 Editors' note: Dr. Findl has financial interests with Abbott Medical Op- tics (Abbott Park, Illinois) and Carl Zeiss Meditec. Dr. Lane has financial interests with Alcon, Bausch + Lomb (Bridgewater, New Jersey), and other ophthalmic companies. Dr. Weinstock has financial interests with Alcon, Bausch + Lomb, and LENSAR (Orlan- do, Florida). Contact information Findl: oliver@findl.at Lane: sslane@associatedeyecare.com Weinstock: rjweinstock@yahoo.com Tip 4: Beware of too many measurements "There's always a tradeoff," Dr. Findl said. "[If you measure more], you can also introduce noise, and that doesn't necessarily make things better." When it comes to the posterior cornea, Dr. Findl takes more of a qualitative look at data to decide what changes, if any, should be made for astigmatic correction. Surgeons also need to consider if cer- tain measurements (beyond just the posterior cornea) seem out of place due to dry eye, an irregular cornea, or other factors. Tip 5: Let patients know that adjustments may take place Even with the best technology, refractive enhancements or IOL exchanges may be needed, Dr. Findl said. If patients know ahead of time, they likely will be more open to the possibility. EW anterior cornea. "The posterior cornea will contribute much less, but there are some odd eyes where it can be quite different [from the anterior cornea]," he said. In those cases, they will consider it in their calculations. There are online calculators such as the Barrett Toric Calculator (available at ascrs.org) that account for posterior cornea measurements, Dr. Weinstock said. Advanced continued from page 52 AT A GLANCE • Most devices should provide accurate measurements for normal healthy corneas, but not all yield identical keratometry values. • To treat eyes with previous corneal surgery, several corneal topographers have developed indices that form an average curvature of the central cornea. • When biometry measurements are unreliable, treat patients aggressively with artificial tears for a week or two and then repeat all measurements. • Toric IOLs are much more precise than LRIs due to the variability in wound healing. by Rich Daly EyeWorld Contributing Writer magnitude and direction of astig- matism, said Richard Tipperman, MD, attending surgeon, Wills Eye Hospital, Philadelphia. "Autokeratometers and manual keratometers can be quite accurate for both the magnitude and direc- tion of astigmatism," Dr. Tipperman said. "The 'sim Ks,' or simulated keratometry readings, provided by topography are not accurate for IOL planning; however, the topography can be very helpful for determining the true axis of astigmatism with providing verification. By perform- ing the keratometry test himself, Dr. Rubenstein can evaluate the quality of the corneal mires to see if there are crisp corneal mires or irregular mires. "Therefore, this is a method of determining the health of the ocular surface and the presence of irregular astigmatism," Dr. Rubenstein said. "If the mires are not crisp and clean, the validity of all the other corneal measurements are diminished." Since astigmatism is a vector, any device that measures astigma- tism will need to measure both the for autokeratometry, manual ker- atometry, topography, and LENSTAR (Haag-Streit, Koniz, Switzerland)/ IOLMaster (Carl Zeiss Meditec, Jena, Germany) in determining corneal curvature and corneal power. "As a rule, I suggest that physi- cians measure the cornea with every modality that they have access to," Dr. Rubenstein said. Dr. Rubenstein relies on manual keratometry combined with IOLMaster and LENSTAR Ks for corneal power, and IOLMaster or LENSTAR values to determine corneal axis, with the corneal map Pearls for improving the selection of keratometry values when determining IOL calculations and astigmatism management L ess than 1% of surgeons are able to achieve refractive outcomes within 0.50 D of the target sphero-equivalent power among at least 90% of their patients. 1 A key to their success is good keratometry. Jonathan Rubenstein, MD, Deutsch Family Professor and vice chairman, Department of Ophthal- mology, Rush University Medical Center, Chicago, said there are roles Tips for selecting the best keratometry values for IOLs continued on page 58 Irregular astigmatism examples

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